The invention relates to methods and devices designed for the control, by means of a first magnitude y, of a second magnitude x, said second magnitude itself being, for each of the values of the magnitude x, a known function of a parameter h which is not under control. In the method, it is assumed that the magnitude y is a one-to-one function of x:y=f(x) and that, for each of the values of the magnitude x such as x.sub.p, x.sub.p is a one-to-one function of a parameter h such that: (x.sub.p)=f.sub.p (h). It also follows therefrom that, for a value of x.sub.p, y is a function of h, y.sub.p =g.sub.p (h).
The method and the device according to the invention can be applied whenever a point with an abscissa value h of the curve representing a second value y.sub.2 (h) can be deduced from the point with the same abscissa value h of the curve representing a first value y.sub.1 (h) by the addition of a value that is a linear function of h. The invention can be extended to an initial control value Y which is a one-to-one function of the magnitude y, controlling a value X which is a one-to-one function of the magnitude x. The functions Y.sub.(y), X.sub.(x) and Y.sub.(X) are not necessarily linear.
The invention relates especially but not exclusively to a voltage control designed for the current bias of a diode with intrinsic zone. In this application, the first magnitude y is a control voltage U, the controlled value x is the bias current I of the diode with intrinsic zone and the parameter h influencing the value of the current is the temperature T of the diode. The need to achieve strict control over the value of the forward bias current I of a PIN or NIP diode with intrinsic zone is encountered whenever it is sought, in a circuit, to control the value of the resistance R of this diode and especially whenever the diode has a controllable attenuator function.
The prior art embodiments cannot be used to obtain control of the bias current I of the diode with intrinsic zone that is well regulated in terms of temperature and has very short switching times between two control values. In the prior art embodiments, either the control is well regulated in terms of temperature, in which case however the switching times are long, or else the temperature regulation is inefficient.